竟然不会Left join了
今天用到Left join 竟然将语法写错了......select * from tt left join tt1 on tt.id=tt1.id id name id name--------------------------1 a 1 a2 b 2 b3 c 3 cselect * from ttleft join tt1on tt.id=tt1.id where tt.id=1id name id name--------------------------1 a 1 aselect * from ttleft join tt1 on tt.id=tt1.id and tt.id=1 id name id name--------------------------1 a 1 a 2 b NULLNULL3 c NULLNULL--left join 以左边表为基础, 扫描右边表匹配的记录select * fromtable1 left join table2 on 条件1 left join table3 on 条件2 left join table4 on 条件3where 条件4
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